Lifter with substantially constant inward jaw pressure



J1me 1965 G. KAPLAN ETAL 3,186,752

LIFTER WITH SUBSTANTIALLY CONSTANT INWARD JAW PRESSURE Filed Dec. 11, 1962 2 Sheets-Sheet 1 FIG INVENTOR;

L'ouls e. KAPLAN June 1, 1965 s. KAPLAN ETAL LIFTER WITH SUBSTAN'I'IALLY CONSTANT INWARD JAW PRESSURE Filed Dec. 11, 1962 2 Sheets-Sheet 2 INVENTORS LOUIS G. KAPLAN Y V ON COUILLAIS United States Patent 3,186,752 LHFTER WETH SUBSTANTIALLY CGNSTANE FENWARD .TAW YRESSURE Louis G. Kaplan, 3% Darrow Sh, Evanston, ill., and Yvon Couillais, 6254 N. Rockwell Ave, (Jhicago, 1111. Filed Jec. Ill, 1962, Ser. No. 243,821 12 Claims. (til. 294-194) The present invention relates to lifters of the opposed jaw type and has particular reference to crane-supported lifters such as are commonly employed for lifting and transporting relatively massive objects such as convolute coil of sheet metal, stacks of flat sheet metal, ingots, castings, slabs and the like. Such lifters are employed at the still mill or foundry for loading purposes and at consumer locations where such objects are distributed throughout the plant for purposes of fabrication. The invention isv specifically concerned with lifters of the gripping type wherein the opposed jaws engage the opposite vertical side surfaces of the object to be lifted with sutficient power that the object is seized and compressed between the jaws, sufiicient inward pressure being exerted that the frictional forces involved predominate over the gravitational forces and, upon hoisting of the lifter bodily upwardly, the object will be raised from its supporting surface for purposes of transportation.

Lifters of the gripping type, as briefly outlined above, are generally of two types insofar as their jaw-impelling mechanism is concerned. In one type, the object-engaging jaws are part of or carried at the lower ends of a pair of ton s arms so that they may swing toward and away from each other. The entire horizontal load-engaging and gripping movement is obtained through suitable linkage operated by vertical displacement or lifting of the supporting structure for the lifter. A pair of common ice tongs constitutes an elementary lifting device of this character. In the other type the object-engaging jaws are horizontally extensible in guideways and external power is required for moving them toward and away from each other. The present invention is applicable to either of these two types of lifters, the principal object being to enhance the gripping action of the jaws, regardless of their mode of motivation.

In both of the above outlined types of lifters, the force required to produce a safe lift is obtained through suitable linkage connected to the lifting force. A relatively smooth and impenetrable object requires a squeezing force considerably in excess of its own weight, and a leverage ratio as high as 6 to l, or even 8 to l, frequently must be used to convert the weight force into squeeze force. In the first mentioned type of lifter,' the entire closing motion of the lifter is obtained through this linkage. If the litter is to accommodate a wide range of object widths, an appreciable vertical displacement of the lifter body is .required. For example, with a gripping leverage ratio of 6 to l, and an opening range of 20 inches, the vertical displacement of the lifter must be on the order of 10 feet. In the second mentioned type of lifter, relative horizontal displacement of the gripping members is obtained by other means, as for example a hand operated screW. A selflocking screw thread must be employed to prevent subsequent jaw separation. The necessary gripping force required to produce a safe lift is obtained in the same manner as in the first type of lifter, namely through a linkage leading to the lifting force. A wedge is a common type of such a linkage but, unfortunately, a wedge which is sufficiently steep as to produce the required gripping force tends to become self-locking and may not release the object at the end of the lifting operation. An eccentric cam is subject to the same limitation. Many other types of linkages have been suggested but each suffers from its own inherent defects or limitations.

EddbJSZ ?atented June Il, 1955 "ice vention consists in the provision of a novel four bar linkage in which one of the bars thereof, or an extension of such bar, carries an object-gripping jaw, the bar proportions, and the point of application of lifting force to such linkage being such that the jaw is causedrto engage the object, at all jaw spreads within its effective gripping range, with a substantially constant gripping force, this force always being in excess of that required to produce the desired lift.

The use of a four bar linkage for suspending either jaw, or the use of dual four bar linkages for suspending both jaws of a lifter is not novel. Such four bar linkages are frequently employed for the purposes of maintaining jaw parallelism throughout the entire range of jaw movements. However, such four bar linkages invariably involve a parallelogram type linkage wherein both pairs of opposite sides of'the quadrilateral structure are parallel and wherein two adjacent pivot pins are fixed. With such a structure, the two movable pivot pins will swing in an arcuate path and, since these movable pins support the actual object-engaging jaw, such four bar linkage arrangements are subject to the same limitations that are present in connection with simple tongstype jaw structures. The four bar linkage mechanism of the present invention is not a parallelogram type of linkage and the design of the various bars thereof is such that the jaws carried thereby will move in will be exerted at the time of lift by reason of a constant gripping factor throughout the effective jaw spread range of the lifter.

In the accompanying two sheets of drawings forming a part of this specification, three illustrative embodiments of the invention have been shown.

In these drawings:

l-" l-G. 1 is a perspective .viewof a lifter embodying the four bar linkage of the present invention, the lifter being of the fixed jaw spread, single linkage type; V

FIG. 2 is a perspective view similar to FIG. 1 showing a modified form of lifter embodying the novel four bar linkage, the lifter being of the adjustable jaw spread, single linkage type;

FIG. 3 is a perspective view similar to FIGS. 1 and 2 showing another modifiedform of lifter embodying the novel four bar linkage, the lifter being of the fixed jaw spread, dual linkage type; and

FIG. 4 is a schematic view illustrating the respective paths of movement of the opposed jaws associated with the lifter of FIG. 3. 7

Referring now to the drawings in detail and in particular to FIG. 1, the lifter shown in this view is of a simplified form and it has been designated in its entirety at it This lifter is comprised of a unitary one-piece combined lifter body and jaw member 12, the body incorporating p in FIG. 1. the reaction jaw is formed separately from the lifter body and isv capable of adjustment toward and away from the j s,1se,752

of vertically elongated designjand having a slot 16 formed in the upper regions thereof designed for reception therethrough of the lifting book 18 associated with a suitable overhead hoist (not shown) and which may be in the form of a power-actuated crane or the like.

The reaction jaw proper i4 is in. the form of a series of relatively sharp-edge tooth-like serrations 24 which are formed adjacent the lower end of one side edge 22 of the member 12, which edge will be hereinafter referred to as the inside edge of the member since it opposes the other jaw of the lifter.

The other jaw proper 24 of the lifter 19 is a movable jaw and it is provided as an integral part of a generally flat floating jaw member 26 which also is preferably a steel plate, and which is of vertically elongated design. The jaw proper 24 similarly assumesthe form of a series of relatively sharp tooth-like serrations 23 which are formed adjacent the lower end of the inside edge 29 of the jaw member 26.

The floating jaw member 26 is connected to the lifter body or fixed jaw member 12 by upper and lower composite link structures 3i? and 32 respectively of the dual or parallel link type, the individual link elements of each structure having their ends secured to the adjacent jaw members by trunnion-like pivot pins, the pins for the upper link structure being designated at 34 and 36 and the pins for the lower link structure being designated at 38 and 40. for convenience of description will be referred to hereinafter simply aslinks) are of different lengths, the upper link 39 being appreciably shorter than the lower link 32. The portion of the lifter body 12 between the pivot pins 4 and 33 constitutes, in effect, an intermediate portion of a four-bar linkage, the other three links being movable and being provided by the upper link 30, the lower link 32, and the part of the jaw member 26 extending between the pivot pins 36 and 40. The jaws 14 and 24 are spaced from each other the maximum separation distance which they are capable of assuming or, in other woods, the jaws are wide open. This raised position of theffloating jaw member 26 is the normal useful position of the jaw member and his contemplated that an object, suchas the slab S, to be engaged between the fixed jaw 14 and the floating jaw 24 shall not be of appreciably less thickness than this maximum separation distance. As will be pointed out in greater detail presently when the operation of the lifter is set forth, the lifter will be fully effective for engaging objects of lesser thickness, in which casethe jaw member 26 will be lowered relative to the jaw member 12. V

In the form of the invention shown in FIG. 2, the four bar linkage arrangement employed remains substantially the same as in theform of the invention shown In this latter'form of the invention, however,

floating jaw so that an initial adjustment of jawspread The two composite-link structures (which 113. Locating pins 125 in the legs 119 cooperate with a series of holes 127 in the body member 112 to the end that the saddle member may be selectively fixed in various transverse positions along the lifter body 112. With such a litter there will be a maximum and a minimum jaw spread for each setting of the reaction jaw or saddle member 121. As will be made clear subsequently when the operation of the various lifters disclosed herein is explained, the opposedjaws 114 and 124 will be effective to produce the necessary gripping force onan object such as the bar B at all jaw spreads between such maximum and minimum jaw spread.

In FIG. 3 a still'further modified formof lifter 210 has been illustrated. Again, the tour bar linkage employed remains substantially the same as in the previously described forms of the invention but it is applied to both of the opposed lifter jaws. Again, also, due to the similarity of parts, reference numerals of a still higher order have been applied to the corresponding parts 216, 218, 2.26, 228 and B as between the structures of FIGS. 1 and 2 to avoid repetition of description.

In the lifter 214?, the basic jaw spread remains fixed. Each of the two jaws proper 214 and 224 are formed on floating jaw members 226 similar to the jaw member 126 and similarly connected to the lifter body 212 by four bar linkages including links 230, 232 and pivot pins 234, 236, 238 and 241?. This form of lifter is designed for use in connection with relatively wide objects such as the block shown at B.

The'princ-iple of operation involved in all three of the lifters 143, 110 and 21% described remains substantially the same and it isbelieved that a description of the operation of one of them will, to a large extent, suffice for them all. Accordingly, the operation of the lifter 210 of FIG. 3 has been schematically illustrated and will be described.

Before entering into a discussion of the operation of the lifters disclosed herein, .it is pointed out that if desired the floating jaw members thereof may be allowed to hang in their free state so that the associated jaws proper will normally assume their condition of minimum jaw spread. However, if desired, means may be provided for causing these floating jaw members to assume a raised position so that the associated jaws will assume a condition of maximum jaw spread. Accordingly, in FIG. 1, a counterweight is carried at the outer ends of a pair of supporting levers 52 which straddle the lifter body 12 and are pivoted as at 53 medially of their ends to the lifter body. A lift pin 54 projects through the floating jaw member 26 adjacent the top thereof and has its opposite ends projecting into slots 56 which are formed may be made to accommodate the handling of objects which vary widely in width. Due to the similarity in f structures, and in order to avoid needless repetition of description, similar characters of reference have been applied to the corresponding parts 120, 124, 128, 130, 132, 134, 136, 138 and 149 as between the structures of FIGS. 1 and 2. a

In FIG. 2 the lifter 11%) includes a lifter body 112 which is generally of horizontally elongated design and which .is provided with an elongated horizontal slot 113 therein, 'the upper edge of the slot being provided with a series i of arcuate recesses 115 therein designed for selective cooperation with the lifting hook118 of the overhead hoist. The reactionjaw proper 114- is inthe form of a steel insert which is supported .on pins 117 which extend between the depending legs 11? of an elongated U-shaped saddle member 121, the. bight portion of which is slidably supported upon the lower straight edge 123 of the slot in the adjacent ends of the levers 52. In FIG. 2, the floating jaw member. 126 is counterbalanced by means of a spring 15% suspended from an overlying extension 151 integrally formed on the lifter body. In FIG. 3,

the floating jaw members 226 are capable of hanging in their free state so that the jaws proper 224 associated therewith Will normally assume their condition of minimum jaw spread, this position being determined by.

means of a pair of limit stops in the form of pins 253 carried at the lower end region of the lifter body 212. It is to be distinctly understood however that, if desired, this form of litter may employ either the counterweight arrangement of FIG. 1 or the spring arrangement of PEG. 2 for counterbalancing the floating jaw members 226.

The geometrical considerations associated with the four bar linkages of FIG. 3 are graphically illustrated in FIG. 4, but this graphical portrayal is equally applicable to the four bar linkages of FIGS. 1 and 2. A similarity of reference numerals assists in identifying the linkage bars with the actual structural parts shown in FIG. 3. The upper and lower links 239 and 232 are represented by the movable bars 230a and 232a. Fixed spans on the lifter framework 212 are represented by the fixed the points 234:: and 238a, while the swinging pivot pins 236 and 249 are represented by the movable points 236a and 240a.

In connection with either of the two four bar linkages, the free pivot point 236a has a locus of movement represented by the dotted line are C1. The free pivot point 240a has a locus of movement represented by the dotted line circle C2. Upon swinging of these points in their respective circular paths, the jaw 224- will describe an irregular figure-eight loop represented in dotted lines a at C3. In the physical construction of FIG. 3, the jaw 224 is limited in its path of travel by interference between the links 230 and 232, the lifter body 21?. and the floating jaw member 226, so that the jaw 22 may not travel throughout its full locus loop and the path of travel which it is capable of traversing is represented in FIG. 4 by the full line portion ab of the loop C3. It will be observed that this path ab is substantially a straight line and that at all points therealong it possesses a considerable component of inward jaw motion. This straight linear path is to be distinguished from conventional tongs type jaw motion which is truly arcuate so that at Wide jaw spreads the direction of motion is largely downward and at small jaw spreads the direction of motion is largely horizontal. In the former instance the gripping pressure is excessive and in the latter instance it is at a minimum. In the case of the linear path of movement represented at ab in FIG. 4, the gripping force is substantially constant at all jaw spreads and i-t is adequate for all contemplated load widths.

In manipulating the lifter 210 of FIG. 3, an operator may, by skillful operation of the overhead hoist, bring the lifter jaws into such contact with the object to be lifted that the weight of the lifter will be effective to cause automatic spreading of the jaws so that the object may be engaged between them. However, to facilitate initial effective jaw-engagement with the object, an operator stationed at lifter level may manually effect the necessary initial jaw spread so that the object may be received between the jaws. Similarly, in the operation of either the lifter 19 of FIG. 1 or the lifter 11d of FIG. 2, an operator may effect initial seizure of the object undergoing lifting by manually moving the floating jaw member 26 or 126, as the case may be, downwardly into contact with the side of the object. As soon as the operator'of the overhead hoist applies a lift. to the lifter body, frictional forces will become effective and the gravitational forces applied to the jaws will operate to establish a firm and powerful grippingaction due to the inward component of motion involved in the substantially straight linear path of motion afforded the floating jaw member by reason of the four bar linkage with which it is associated and which motion has been exemplified by the portion ab of the locus curve C3 in FIG. 4.

In connection with the foregoing description, it is pointed out that the term tongs as employed herein is intended to refer to any arrangement consisting of two arms pivoted to each other or to spaced points, and which are capable of swinging movement toward and away from each other for gripping an object therebetween, this definition including arms which are pivoted medially of their ends or which are pivoted at their ends. It also is pointed out that theterm four bar linkage is in tended to refer to an articulated linkage including four bars which are pivoted at adjacent ends to provide a closed quadrilateral loop which may define aparallelogram, a trapezium or a trapezoid.

The terms maximum jaw spread and minimum jaw spread as employed herein do not necessarily refer to absolute overall jaw spreads. They refer rather to the portions of any given jaw spread which are occasioned by the use of the present four bar linkages. For example, in a horizontally extensible type lifter, the absolute jaw spread may vary from a position of jaw contiguity to several feet. The lateral jaw displacement occasioned by the use of the present four bar linkage is measured in inches so that when such a linkage is applied to a horizontally extensible type lifter, the jaws may be adjusted for a Wide overall jaw spread but, for that particular given jaw spread, there will be a maximum and a ruinimum jaw spread, occasioned solely by the range of movement offered by the four bar linkage.

Various other modifications of the invention are contemplated within the scope of the appended claims. For

example, in various commercial embodiments of the lifter the counterbalancing means may be dispensed with and the jaws latched in their raised positions, the latch means being operated by remote control from the overhead hoist. Therefore, only insofar as the invention has particularly been pointed out in the accompanying claims is the same to be limited.

Having thus described the invention, what we claim and desire to secure by Letters Patent is: a

l. A lifter of the. opposed gripping jaw type comprising: a lifter body, a first object-gripping jaw carried on said body, means on said lifter body establishing a four bar linkage of the type wherein the four bars thereof are pivotally connected together at adjacent ends to provide a closed quadrilateral structure, the four bars of said linkage including an intermediate portion of the lifter body,

a movable jaw-supporting member opposite to said intermediate portion, a movable upper link connecting the upper end of said intermediate portion to the upper end of said jaw-supporting member, and a lower movable link connecting the lower end of said intermediate portion to the jaw-supporting member at an intermediate point thereon, the distance between the upper and lower links on the jaw-supporting member being less than twice the distance between the upper and lower links on the lifter body, the lower region of said jaw-supporting member projecting downwardly and constituting an extension of the jaw-supporting member which lies outside the confines of said articulated quadrilateral structure, a second object-gripping jaw on said extension and opposing said first jaw, the efiective length of said upper link being less than the effective length of the lower link whereby the jaw-supporting member is capable of movement between an elevated position and a lowered position for varying the effective distance between said jaws and the second object- 7 gripping jaw carried thereby will move in a substantially straight linear path.

2. A lifter of the opposed gr'pping jaw type as set forth in claim 1, wherein the length of said intermediate portion f the lifter body is substantially equal tov the distance between the upper end of said jaw-supporting member and said intermediate point thereon.

3. A lifter of the opposed gripping jaw type as set forth in claim ll, wherein the length of said intermediate portion of the lifter body is substantially equal to the distance between the upper end of said jaw-supporting member and said intermediate point thereon, and wherein when said upper and lower links are parallel, the linkage involved is in the form of an upright trapezoid.

4. A lifter of the opposed gripping type as set forth 7 in claim 1, wherein said first object-gripping jaw is fixedly disposed on the lifter body.

5. A lifter of the opposed gripping jaw type comprising: a lifter body, a first jaw-supporting member movably mounted on said lifter body for selective positioningat 4 different horizontally spaced regions along the lifter body,

means on said lifterbody establishing a four bar linkage, the four bars of said linkage including an intermediate portion of the lifter body, a second jaw-supporting member opposite to said intermediate portion, an upper link 7 connecting the upper end of said intermediate portion to the upper end of said secondjaw-supporting member, and a lower link connecting the lower end of said intermediate portion. to the second jaw-supporting member at an intermediate point on the latter, the lower region of said second jaw-supporting member projecting downwardly and constituting an extension of the jaw-supporting member which lies outside the confines of said four bar linkage, a pair of opposed jaws on said first jaw-supporting member and extension respectively, the distance between the connection of the upper and lower links on said second jaw-supporting member being less than twice the length of said intermediate portion of the lifter body and the effective length of said upper link being less than the efiective length of said lower link whereby the second jaw supporting memberis capable of movement between an elevated position and a lowered position to vary the effective distance between said jaws with the jaw on said extension moving in a substantially straight linear path.

6. A lifter of the opposed gripping jaw. type as set forth a in claim 5, including, additionally, means for securing the first jaw-supporting member in selected positions of adjustment.

7. A lifter of the opposed gripping type as set forth in claim 5, wherein the length of said intermediate portion 7 of thelifter body is substantially equal to the distance between the upper end of said second jaw-supporting member and said intermediate point thereon.-

S. A lifter of the opposed jaw gripping type comprising: a lifterbody in the form of a generally flat relatively thick plate having an elongated horizontal slot therein, an inverted U-shaped saddle member having abight portion slidably supported on the lower edge of said slot and provided with legs which straddle the plate and depend below the lower edge thereof, a first object gripping jaw carried at the lower depending ends of said legs, means on said lifter body establishing a four bar linkage of the type wherein the four bars thereof are pivotally connected together at adjacent ends to provide a closed quadrilateral articulated loop, the four bars of said linkage including an intermediate portion of the lifter body, a movable jaw-supporting member opposite to said intermediate portion, an upper link connecting the upper end of said intermediate portion to the upper end of said jawsupporting member, and a lower link connecting the lower end of said intermediate portion to the jaw-supporting memberat an intermediate point on the latter, the lower region of said jaw-supporting member projecting downwardly and constituting an extension of the jaw-supporting 7 member which lies outside the confines of said articulated whereby the same may be engaged by an overhead hoist,

' means on said lifter body establishing two similar four quadrilateral loop, a second jaw on said extension and opposing the first jaw, the distance between the connection of the upper and lower links on said jaw-supporting member'being less than'twice the length ofsaid intermediate portion of the lifter body, the effective length of said upper link being less than the effective length of the lower link whereby the jaw-supporting member is capable ,of movement between an elevated position and a lowered position to vary the effective distance between said. jaws with the jaw on said extension moving in a substantially straight linear path, means for securing said saddle member in selected positions along said slot, the upper edge of said slot being provided with a series of recesses designed for selective reception therein of a lifting hook by means of which the lifter may be lifted bodily, and means for counterbalancing the weight of said jaw-supporting member and maintaining the same in its elevated position. a

9. A lifter of the opposed jaw gripping type as set forth in claim 8, wherein said counterbalancing' means comprise an extension on the lifter body overlying said jawsupporting member, and a spring connected to said extension and jaw-supporting member.

bar linkages of the type wherein the four bars thereof are plvotally connected together at adjacent ends to provide a closed articulated quadrilateral loop; the four bars of each linkage including an intermediate portion of the lifter body, a movable jaw-supporting member opposite to said intermediate portion, an:upper link connecting the upper end of said intermediate portion to the upper end of said jaw-supporting member, and a lower link connecting the lower end of saidintermediate portion to an intermediate point on said jaw-supporting member, the lower region of each jaw-supporting member projecting downwardly and constituting an extension of the jaw-supporting member which lies outside the confines of its associated articulated quadrilateral loop, a jaw on each of said downwardly projecting extensions, the jaws of the two extensionsopposing each other, the distance between the connection of the upper and lower links on said jaw-supporting member being less than twice the length of said intermediate portion of the lifter body and the effective length of each upper link being less than the effective length of its associated lower link whereby the jaw-supporting members are individually movable between elevated and lowered positions to cause the jaws on the extensions thereof to move in respective substantially straight linear paths which are inclined downwardly and inwardly toward each other.

11. A lifter. of the opposed gripping jaw type comprising: a lifter body having means associated therewith whereby the same may beengaged by an overhead hoist, means carried by said lifter body establishing a pair of spaced apart intermediate portions, means including said intermediate portions establishing a pair of four bar linkages; the four bars of each linkage including, in addition to one of the portions, 21 jaw-supporting member opposite to said one'portion, an upper link pivoted to the upper end of said one portion and to the. upper end of said jaw-supporting member, and a lower link pivotally connected to the lower end of said one portion and to said jaw-supporting member at an intermediate point on the latter, the lower region of said jaw-supporting member projecting downwardly and constituting an extension of the jaw-supporting member which lies outside the .confines of the associated four bar linkage, a pair of opposed jaws on said extensions,-the distance between the pivot points of the upper and lower links on the jawsupporting member being, less than twice, the distance between the pivot points of the upper and lower links on the lifter body, the effective length ofrthe upper link of each four bar linkage being less than the effective length of the lower link of suchlinkage; whereby the jaws of the two four bar linkages are constrained to move .in respective linear paths which are substantially straight and which are inclined downwardly and inwardly with respect to each other.

12. Alifter of the opposed gripping jaw type-as set forth in claim 11 includingadditionally an object-penetrating gripping point on each jaw.

References Cited by the Examiner UNITED STATES PATENTS 1,317,291 9/19 Heckman 244104 1,583,611 5/26 Seely 269-208 2,67 9,379 5/54 Peterson 294-l 04 FOREIGN PATENTS 182,43 8 3 07 Germany.

ROBERT B. REEVES, Primary Examiner,

' A. H. NIELSEN, ERNEST A. FALLER, Examiners. 

1. A LIFTER OF THE OPPOSED GRIPPING JAW TYPE COMPRISING: A LIFTER BODY, A FIRST OBJECT-GRIPPING JAW CARRIED ON SAID BODY, MEANS ON SAID LIFTER BODY ESTABLISHING A FOUR BAR LINKAGE OF THE TYPE WHEREIN THE FOUR BARS THEREOF ARE PIVOTALLY CONNECTED TOGETHER AT ADJACENT ENDS TO PROVIDE A CLOSED QUADRILATERAL STRUCTURE, THE FOUR BARS OF SAID LINKAGE INCLUDING AN INTERMEDIATE PORTION OF THE LIFTER BODY, A MOVABLE JAW-SUPPORTING MEMBER OPPOSITE TO SAID INTERMEDIATE PORTION, A MOVABLE UPPER LINK CONNECTING THE UPPER END OF SAID INTERMEDIATE PORTION TO THE UPPER END OF SAID JAW-SUPPORTING MEMBER, AND A LOWER MOVABLE LINK CONNECTING THE LOWER END OF SAID INTERMEDIATE PORTION TO THE JAW-SUPPORTING MEMBER AT AN INTERMEDIATE POINT THEREON, THE DISTANCE BETWEEN THE UPPER AND LOWER LINKS ONTHE JAW-SUPPORTING MEMBER BEING LESS THAN TWICE THE DISTANCE BETWEEN THE UPPER AND LOWER LINKS ON THE LIFTER BODY, THE LOWER REGION OF SAID JAW-SUPPORTING MEMBER PROJECTING DOWNWARDLY AND CONSTITUTING AN EXTENSION OF THE JAW-SUPPORTING MEMBER WHICH LIES OUTSIDE THE CONFINES OF SAID ARTICULATED QUADRILATERAL STRUCTURE, A SECOND OBJECT-GRIPPING JAW ON SAID EXTENSION AND OPPOSING SAID FIRST JAW, THE EFFECTIVE LENGTH OF SAID UPPR LINK BEING LESS THAN THE EFFECTIVE LENGTH OF THE LOWER LINK WHEREBY THE JAW-SUPPORTING MEMBER IS CAPABLE OF MOVEMENT BETWEEN THE ELEVATED POSITION AND A LOWERED POSITION FOR VARYING THE EFFECTIVE DISTANCE BETWEEN SAID JAWS AND THE SECOND OBJECTGRIPPING JAW CARRIED THEREBY WILL MOVE IN A SUBSTANTIALY STRAIGHT LINEAR PATH. 